Close ratio gearset for Tamiya...???

[Espeefan]

A close ratio 3 speed gearset might go over better then a 9 speed. If the calculated ratios were done so that no one needed aux gear reducers, it would be a big hit.

[Aero 9000]

Originally Posted by Espeefan

A close ratio 3 speed gearset might go over better then a 9 speed. If the calculated ratios were done so that no one needed aux gear reducers, it would be a big hit.

You cannot get ratios into the Tamiya box that would eliminate the add on3:1 gear reducers commonly used. The gears would simply be too large.
The 44 tooth used on 1st is the biggest gear that will fit (thats why Tamiya use it) and the 13 tooth that drives it on the counterhaft is the smallest that is practical considering the wear factor and the fact it is also used as a spline for the primary reduction.

So the biggest ratio between the countershaft and the clustershaft is 3.38:1, if you then use the 10 tooth pinion on the motor runnining on the primary reduction gear of 36 teeth that ratio is 3.6:1 .

3.6 x 3.38 = 12.168:1 overall reduction. Then reduced 3 times further by the 3:1 aux reduction box, for a total of 36.5:1 in first gear.

Leaving the 3.6:1 primary reduction aside, 3.38:1 from first gear times the 3:1 aux reduction gives 10.14:1 .....to acheive a 10 to 1 reduction in a single step given the smallest gear you can feasably use has 13 teeth, the driven gear would need 130 teeth, that gear would be wider than the truck.

So acheiving large ratios inside the box to eliminate aux gears is not feasable.

You could add another 3:1 to the primary reduction by adding extra gearing from the motor but that would considerably increase the torque that the counter and clustershaft gears (and more importantly the drive dogs) would encounter.

The Tamiya plastic gears and selector mechanisms are a good set up for high speed use but i doubt they would last well absorbing high torque, so extra primary reduction is not a good idea.

So larger cluster gears are out.....increased primary reduction is out.....
That leaves aux reduction....

A aux reduction that bolted straight to the back of the Tamiya box would need 2 pairs of gears to keep the output shaft at the same level as standard.
That is likely to cost at least as much or more than the aux boxes that are currently used and have no advantage over them.........



These are also some of the reasons why the 9 speed developed into what it is.....

[Lil Giants]

Originally Posted by Aero 9000

You could add another 3:1 to the primary reduction by adding extra gearing from the motor but that would considerably increase the torque that the counter and clustershaft gears (and more importantly the drive dogs) would encounter.

The Tamiya plastic gears and selector mechanisms are a good set up for high speed use but i doubt they would last well absorbing high torque, so extra primary reduction is not a good idea...

I have proved it for years that the Tamiya 3spd can handle 3:1 aux primary gearing.

I have a 6wd GL weighted down to 17lbs with 1.9 heavy grip tires pulling a 35lbs bellydump trl up a 12 degree incline for literally hundreds of miles over the last 5yrs or longer.. it's the original trans in that trk & I have never replaced a gear or dog clutch in it. This trk runs an FM radio system that glitches on occassion while under full load, so the 3spd trans can take the shock of an abrupt start/stop as well.

What's nice about transplanting the hilift t-case is the added 2.1:1 additional reduction on the back of trans for a wee bit more torque & slow speed control of the trk. A reasonable compact, lower profile setup. I run the incline in 2nd gear all the time, 3rd gear for bobtailing and 1st for maximum traction in soft ground conditions so as not to slip a wheel & dig a hole.